Ground breaking research on insecurity of brainwallets by Ryan Castellucci was presented at DefCon 2015 on 7 August 2015:

• At least 733 BTC (about 200,000 USD) was at one time (more or less recently) exposed to immediate theft.
• Many very complex passwords such as “No need to worry, my accountant handles that” already cracked.
• A dozen of active thieves already in operation.
• A super-fast brainwallet cracker is available to download, more thefts to come!

See the slides.